8th Grade Science – Professor Shai
Fractional Distillation Lab
Section 5.1 – Page 90
Under Construction
Introduction
Fractional distillation is a way
to separate liquids in a mixture by using the characteristic property
of their boiling points. Essentially, you boil off the liquid and
collect the gas by condensing it in cooled test tubes. If the
different liquids in the mixture have distinct boiling points, then
each will boil out at different temperatures. The trick is
knowing when to switch test tubes. This can be determined by
using a thermometer, recording
temperatures, graphing them and figuring out the different boiling
points - i.e., when the graph goes flat.
Goals
The
goals of this experiment are to distill a mixture of fluids, separate
the components, and perform tests to identify each one.
Method
This is a long experiment that will take
you about a week to complete. It is an important experiment
because you will need
to use these techniques in the sludge project coming up. It is
divided into parts A-F, and you should attempt to complete at least one part each day.
Part A: Test the mixture in four
ways:
- Odor (strong, weak,
none). Smell it and take a vote in your group.
- Flammability (yes,
no). Place some
liquid on paper
and try to burn it (call me over). You should try it with burner
fuel
and water first to get a benchmark of flammable versus
inflammable.
- Density (numerical
value in g/cc). Measure
the mass and volume carefully since it is easy to be sloppy and ruin
your results.
- Solubility of Sugar in Liquid (yes,
no). Use just
.05 grams into 1 cc
for testing. If you can get it to dissolve, then you can conclude
soluble. Make sure to mix well and be patient.
Record all your results.
Write them on the board. Answer all blue questions in the
book.
Technique: For the next two parts you will use the apparatus
shown on page 91 of your book. Here are some notes on
technique. Note that the bulb of the thermometer is above the
boiling liquid in Part B, and below it in Part C. Also, note that
the end of the rubber tube in the collecting test tubes is below the
level of the cooling liquid and above the level of the collected
liquid. This prevents distilled liquid from going back up the
rubber tube into the boiling test tube. Finally, to get good results
you need to have even steady heating. To make sure you don't
"bump" the temperature, use fresh boiling chips every time you start a
new boil, and adjust the screen under the tube to allow more or less
heat as needed.
Part B: Do a dry-run
distillation on 5cc's of the mixture to determine the number of
component liquids and boiling
points.
Record the temperature of
the vapors every
minute. The thermometer should be above the boiling fluid in the
vapors. Graph the temperature versus time and
determine how many distinct boiling points there are, and what
temperatures they are at. Answer all blue questions in the
book.
Part C: Distill 25 cc's of the mixture into collecting
tubes.
Verify
the temperatures by recording the temperature of the liquid (not the vapors) every
minute, and graph the results. The thermometer should be in the
boiling liquid this time. You should collect a new tube a few
seconds after the boiling point temperature of each substance is
reached, i.e., just to the right of the start of each flat section on
your graph. Also, start a new tube after each time the
temperature starts to rise again, i.e. just to the right of the
end of each flat section on your graph. This allows you to
capture each liquid as well as a mixture of each pair of liquids.
For example, if your mixture is made up of just two liquids, I and II,
you collect 3 tubes: I, I and II, and II. If your mixture had 3
liquids originally I, II, III, then you collect 5 tubes: I, I and
II, II, II and III, and III, Compare your temperature graph with
the graph from Part B. Label
each collecting tube with your group name and the appropriate I or II
etc. When you are finished, test each liquid (also called
fraction) for odor and
flammability. Record all results. Save your samples.
Parts D-E: For each test tube of fluid you collected:
- Test whether or not sugar is soluble in your liquid. Write
results on the board.
- Measure the density. Write results on the board.
- Boil the whole sample and recollect it, creating a
vapor-temperature graph (thermometer above the liquid) as you proceed.
Part F: Make a chart summarizing all your results. Write results
on the board. For each test tube, your chart should include:
- Odor (Strong, Weak, None)
- Flammability (Yes, No)
- Density (Numerical value in g/cc)
- Solubility of Sugar (Yes, No, Slightly)
- Boiling Point (Numerical value in degrees Celsius, or not
constant).
Answer all blue questions on page 92 in the book.
Conclusions
The original mixture was
made up of two liquids, isopropanol (rubbing alcohol) and water.
Test tube I was mostly isopropanol, test tube I-II was a mixture of
isopropanol and water, and test tube II was mostly water. A chart
showing sample good results is shown below:
Liquid
|
Odor
|
Flammability
|
Density
g/cc
|
Solubility
of Sugar
|
Boiling
Point in C
|
Original
Mixture
|
Weak
|
Yes
|
.91
|
Soluble
|
not
constant
|
Tube
I
|
Strong
|
Yes
|
.84
|
Insoluble
|
80
|
Tube
I-II
|
Weak
|
Yes
|
.93
|
Slightly
Soluble
|
not
constant
|
Tube
II
|
None
|
No
|
1.03
|
Soluble
|
100
|
Book Problems
Do problems 1-3,
on page 92.
Ask me for help if you are
not sure how to
do them.